1. Field of the Invention
The present invention relates to an exhaust muffler for an engine, and more particularly to an exhaust muffler in which a control valve for controlling the flow of exhaust gases is provided in a muffler main body, or on an exhaust gas discharge pipe.
2. Description of the Related Art
An exhaust muffler disclosed in JP-A-8-200039 is known as the exhaust muffler described above.
Although the control valve of the aforesaid conventional exhaust muffler is advantageous in that the flow resistance of exhaust gases can be set relatively freely by varying the opening area of a valve body in response to change in the pressure of exhaust gases, the control valve has a problem in that the weight, size and production cost thereof increase are large due to the fact that the control valve includes a number of components such as a valve housing, a rotating shaft, a valve body, a rotationally biasing spring, an axially biasing spring, a case member for forming a spring chamber and a cover.
The invention was made in view of the aforesaid situations, and an object thereof is to provide a control valve for an exhaust muffler that includes as few components as possible so as to reduce the weight, size and production cost thereof.
With a view to attaining the above and other objects, according to a first aspect of the invention, there is proposed an exhaust muffler comprising a muffler main body, an exhaust gas induction pipe for inducting exhaust gases into the muffler main body, an exhaust gas discharge pipe for discharging the exhaust gases within the muffler main body to the outside, and a control valve provided in the muffler main body or on the exhaust gas discharge pipe for controlling the flow of the exhaust gases. The control valve is constituted by a first tubular body having an exhaust gas inlet opening, at one side thereof, through which exhaust gases flow in an axial direction from the one side to a second, opposite, side of the first tubular body, a second tubular body adapted to axially moveably fit on or in the first tubular body and having a pressure receiving surface for receiving the pressure of exhaust gases flowing thereinto from the exhaust gas inlet opening, wherein the pressure receiving surface is located adjacent to the second end of the first tubular body, and a spring disposed in an annular gap formed between the two tubular bodies, at a portion where the first tubular body fits on or in the second tubular body, for biasing the second tubular body towards the one end in the axial direction. When the second tubular body receives the pressure of the exhaust gases so flowing thereinto at the pressure receiving surface and then moves towards the second end against the biasing force of the spring, the exhaust gases within the first tubular body flow out of communicating holes formed in an outer circumferential surface of the second tubular body to the outside of the second tubular body.
According to the above construction, since the control valve can be constituted by only three membersxe2x80x94such as the first tubular body, the second tubular body and the springxe2x80x94the size, weight and production cost of the control valve can be reduced. Additionally, since the first and second tubular bodies are disposed one inside the other coaxially, the axial dimension of the control valve can be reduced to thereby save and reduce the space required for installation thereof.
According to a second aspect of the invention, there is proposed an exhaust muffler as set forth in the first aspect, wherein the first tubular body is constituted by a communicating pipe for providing a communication between a plurality of silencing chambers formed by partitioning the interior of the muffler main body, or the exhaust gas discharge pipe.
According to the above construction, since the communicating pipe for providing a communication between the plurality of silencing chambers, or the exhaust gas discharge pipe, is used as the first tubular body, the number of components can be reduced to thereby reduce further the size, weight and production cost of the control valve.
According to a third aspect of the invention, there is proposed an exhaust muffler as set forth in the first or second aspect, wherein the spring is constituted by a compression coil spring whose outside diameter is variable relative to an axial direction thereof, whereby the spring is adapted to come into contact with at least one of the first and second tubular bodies at an outer or inner circumferential portion thereof.
According to the above construction, since the spring is constituted by the compression coil spring whose outside diameter is variable relative to the axial direction thereof, whereby the spring is adapted to come into contact with at least one of the first and second tubular bodies at the outer or inner circumferential portions thereof, the resonance phenomenon of the spring can be prevented by virtue of a friction force acting on the contact portion.
Additionally, according to a fourth aspect of the invention, there is proposed an exhaust muffler as set forth in any of the first to third aspects of the invention, wherein as the amount of movement of the second tubular body towards the second end of the first tubular body increases, the opening areas of the communicating holes in the second tubular body increase.
According to the above construction, since the flow rate of the exhaust gases passing through the control valve increases gradually, or in a stepped fashion, as the engine load increases, the target ratio between the exhaust gas noise silencing effect and the engine output reduction suppressing effect can be controlled gradually or in a stepped fashion from a lower engine-loaded state in which priority is given to the improvement in the exhaust gas noise silencing effect, to a higher engine-loaded state in which priority is given to the improvement in the engine output reduction suppressing effect. Therefore, the ratio between the two effects can be automatically varied, as the driver expects, in response to a change in engine load, thereby making it possible to enhance the performance of the exhaust muffler.
Note that: first, second and third silencing chambers 29 to 31 in the embodiments correspond to the silencing chambers of the invention; a second communicating pipe 35 and a sub-exhaust gas discharge pipe 45 in the embodiments correspond to the first tubular body of the invention; a valve body 37 in the embodiments corresponds to the second tubular body of the invention; and a coil spring 39 in the embodiments corresponds to the spring of the invention.